Epilepsy is a neurological disorder caused by excessive excitation of electric activity in the brain and is diagnosed by a characteristic electroencephalogram (epileptic electroencephalogram). The prevalence of epilepsy is high, reaching about 1% of the total population. Treatment methods for epilepsy mainly include drug therapy, and more than 20 types of therapeutic drugs for epilepsy are used in clinical settings (Non-Patent Document 1). However, it is known that these existing therapeutic drugs for epilepsy do not work for about 30% of patients with epilepsy. From such a background, therapeutic drags for “refractory epilepsy” for which existing drugs do not work are currently needed.
Since epilepsy is caused by excessive neural excitation, therapeutic drugs for epilepsy are mostly targeted to molecules that control electrical activity. Specific examples include ion channels, synaptic receptors, and neurotransmitter transporters (Non-Patent Document 2). On the other hand, it is clinically known that “diet therapy” called ketogenic diet treatment is effective for some epilepsy patients for whom these existing drugs do not work (Non-Patent Document 3). Recently, anti-epileptic mechanisms mediated by the ketogenic diet have been revealed one after another (Non-Patent Documents 4 to 6). That is, if a drug acting on the energy metabolic pathway is developed, it is promising as a drug for refractory epilepsy.
Stiripentol (CAS: 49763-96-4, 4-dimethyl-1-[(3, 4-methylenedioxy)-phenyl]-1-penten-3-ol, see formula (I) below) is an antiepileptic drug. Stiripentol was first developed as a brain disease drug (Patent Document 1), and it was then shown to be effective for Dravet syndrome (one of childhood epilepsies) which is one of refractory epilepsies (Non-Patent Documents 7 and 8). Stiripentol is now clinically used as a drug for Dravet syndrome in Europe (approved in 2007) and Japan (approved in 2012) under the trade name of Diacomit. However, although stiripentol therapy was successful in Dravet syndrome, it has not been successful at present in clinical trials for other epilepsies (especially adult epilepsies) (Non-Patent Document 9).
Recently, it has been reported that stiripentol is an inhibitor of lactate dehydrogenase (LDH) (Patent Document 2). Lactate dehydrogenase is a “metabolic enzyme” existing “on the energy metabolic pathway” and carrying out interconversion between lactate and pyruvate. Lactate dehydrogenase inhibitors themselves have been developed mainly for the purpose of development of antimalarial drugs (Non-Patent Documents 10 and 11), and development of anticancer drugs (Non-Patent Documents 12 and 13). However, it is unknown whether these lactate dehydrogenase inhibitors have antiepileptic effects. That is, at this time, stiripentol is the only “antiepileptic drug” having “lactate dehydrogenase inhibitory action”.
